Security concerns have prompted a federal prosecutor in Houston to withdraw from a big racketeering case involving the Aryan Brotherhood of Texas, which has been a focus of the investigations into the slayings of the Kaufman County district attorney and an assistant.

Assistant U.S. attorney Jay Hileman on Tuesday notified attorneys representing 34 defendants, The Dallas Morning News and TPM reported. A Justice Department prosecutor in Washington, D.C., who is already involved in the case will take over.

Neither the Morning News nor TPM specified the security issues or say whether Hileman or his family had been threatened.

"He's obviously made a decision based on something," said defense attorney Richard O. Ely II, who added that he had been threatened when he was a prosecutor.

One of the group's former top leaders, Terry Sillers, has pleaded guilty and agreed to cooperate in the case, which is being prosecuted in Houston. Authorities have him in protective custody.

The neo-Nazi gang has come under renewed scrutiny since Kaufman County District Attorney Mike McLelland and his wife, Cynthia, were found dead in their home Saturday. Investigators said he had been shot 20 times. In January, country prosecutor Mark Hasse was gunned down in a parking lot not far from the courthouse.